Note: Descriptions are shown in the official language in which they were submitted.
73 5
METHOD OF MANUFACTURING A ROCK BIT CONE
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufactur-
ing a rock bit cone rotatably supported by each of a plurality
of bearing pins extending centripetally obliquely equiangularly
from a rock bit body and having a number of teeth on a conical
outer surface thereof.
Petroleum and natural gas exist, generally beneath a cap
rock. Therefore, in order to prospect for them and to mine
them, it is necessary to drill a rock layer by using a drilling
facility provided on the ground or sea surface.
As the rock bit for drilling rock layer, blade bit, cone
bit and diamond bit etc. have been known. Among others, the
cone bit has been widely used.
The conventional cone bit comprises a rock bit body
formed in an upper portion thereof with a thread into which a
drill collar of a drill pipe is screwed, a plurality o~ equian-
gularly spaced bearing pins extending centripetally obliquely
from an inner face of a leg portion formed in a lower portion
thereof. Each bearing pin supports rotatably a cutter in the
form of a cone having a conical outer surface in which a number
of teeth are implanted.
In drilling a rock layer, a drill collar mounted on a
lower end of a drill pipe is screwed onto the threaded portion
of the bit body and the drill pipe is rotated by a rotary table
of a drilling rig arranged on the ground or sea surface J SO
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that the cones are rotated around the bearing pins by means of
contacts between the teeth thereof and the rock layer. Thus,
portions of the rock layer are crushed, turned up and kicked
out by the teeth. On the other hand, high pressure mud is sup-
plied through the drill pipe to the cone bit by a mud pump pro-
vided in the drilling rig. The high pressure mud functions to
lubricate the teeth of the cones and carry the crushed rock
portions through an annular space formed between an outer sur-
face of the drill pipe and a wall of a drilled hole up to the
surface of ground or sea.
Therefore, the teeth must be of highly hard material. A
TCI (tungsten carbide insert) bit having implanted inserts each
of tungsten carbide or a milled tooth bit having teeth each
prepared by machining and then hard-facing the surface thereof
with a hard metal has been used conventionally. The TCI bit is
usually manufactured by forming a cone body by forging, boring
holes in places of a surface thereof, in which cylindrical in-
serts are to be implanted, by a boring machine and pressing
these inserts into the respective holes. Therefore, it re-
quires a number of manhours and it becomes very e~pensive, ne-
cessarily~ On the other hand, the hard-facing technique which
is necessary to manufacture the milled tooth bit usually con-
tains some uncertainty and it is very difficult to obtain a
uniform hard metal layer on the teeth. Even if a uniform layer
is provided, it is usually peeled off easily by mechanical
shock. Further, the milled tooth bit is also expensive.
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SUMMARY OF THE INVENTION
An object of -the present invention is to provide a method
of manufacturing a cone which is stable in performance and in-
expensive.
According to one aspect of the present invention, the
above object is achieved by pressure-casting of a cone body
having teeth by using a casting mold having a molding surface
configuration including a cone body portion and tooth portions
and machining only a portion thereof to be supported by a
bearing pi
n.
Acco
rding to another aspect of the present invention, the
above obie
ct is achieved by the pressure-casting using a simi-
lar mold t
o that used in the first aspect except that prelimi-
nary prepa
red inserts of highly hard alloy such as tungsten
carbide ar
e positioned in desired places on the molding surface
such that
when cast, a cone has the inserts having root por-
tions embe
dded in the cone body.
Acco
rding to a third aspect of the present lnvention, the
same casti
ng mold as that used in the first method is used. A
very hard,
molten metal is firstly poured thereinto and by
pressure-c
asting method to form a hard metal portions on at
least tip
portions of the teeth, and then a molten tough metal
is poured
and by pressure-casting method so that the second
metal is a
dhered firmly to the first metal to form a cone body
of the tou
gh metal having teeth at least the end portions of
which are
formed of the hard metal.
Acco
rding to a fourth aspect of the present invention~ a
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'735
similar casting ~old to that used in the first method is used.
Tooth pieces of same material as the tough metal forming a cone
body are preliminary prepared and are supported in recesses on
an inner surface of the mold which correspond to the teeth, re-
spectively, such that root portions of the tooth pieces pro-
trude from the inner surface of the mold and a predetermined
space is provided between a surface of each recess and an outer
surface of the tooth piece. Then, a molten hard metal is
poured into the mold by pressure-casting method so that the
hard metal fills the predetermined space. Finally, the molten
tough metal is poured thereinto by pressure-casting method to
form the cone body. According to this fourth method, the cone
body molded has the teeth which are covered by the hard metal.
According to the first method, it is possible to cast the
cone body and the teeth simultaneously and, particularly, the
teeth which function to crush and turn-up a rock can be formed
precisely and rigidly with a minimum number of manhours compar-
ing with the conventional method. Therefore, it is possible to
provide a required performance and strength of the cone bit.
Further, since the cone body and the teeth are integral com
pletely, there is no peeling off problem and/or dropping-out
problem of the teeth. ~hen the surface of the teeth are hard-
faced on demand, there is no need of machine cutting of the
teeth having complicated con~iguration which is necessary in
producing the conventional milled tooth bit.
According to the second method of the present invention,
the cone body having a precise configuration is easi~y produced
with the root portions of the inserts being ~irmly embedded in
;V735
the cone body. Therefore, the TCI bit can be manufactured eas-
ily comparing with the conventional method, with the inserts
being retained reliably by the cone bit. The reliability of
retaining the inserts may be further improved by shaping each
insert such that the root portion thereof provides a means to
increase a resistance against a pulling-out force applied
thereto.
According to the third method, the hard metal layer is
formed on a predetermined area of the insert including the top
end thereof and this layer is adhered reliably to the root por-
tions of the teeth casted integrally with the cone body.
According to the fourth method of the present invention,
a predetermined surface area of each of the teeth protruding
Prom the surface of the cone body is completely covered with
the hard metal longer and the root portion of the tooth piece
constituting a core of the tooth is completely integral with
the cone body. Therefore, a resultant rock bit cone is excel-
lent in strength and performance.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a perspective view of a casting mold to be used
in performing an embodiment of the method according to the
present invention;
Fig. 2 is a cross sectional plane view of a portion of
another example of the casting mold;
Fig. 3 is a cross sectional view of a casting mold to be
used in a second embodiment of the method according to the
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present invention;
Fig. 4a to 4e show side views of inserts which have root
configurations ef~ecti~/e to prevent the inserts from dropping
out, respectively;
Fig. 5 is a partially cross sectioned side view of a cone
manufact~lred according to the first method of the present in-
vention;
Fig. 6 is a partially cross sectioned side view of a cone
manufactured according to the second method of the present in-
vention;
Fig. 7 is a cross section of a portion of the casting
mold for explanation of the third method of the present inven-
tion; and
Fig. 8 is a cross section of a portion of the casting
mold for explanation of the fourth method of the present inven-
tion.
DETAILED DESCRIPTION OF THE PREFERED EMBODIMENTS
Fig. 1 shows an example of a casting mold for performing
the present invention. In Fig. 1, a centrifugal casting mold
lO has a molding surface composed of a cone body defining sur-
face portion 12 and teeth defining surface portions 13. The
mold lO is rotatably supported around an axis 11 of the cone
with an apex of the cone body defining surface portion being
down. The casting is performed by pouring molten metal
thereinto while rotating it at a suitable speed. The rotating
speed should be selected such that an optimum pressing force is
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735
obtained according to a balance between a centrifugal force and
gravity. With a proper selection of the rotating speed, the
molten metal fills a necessary space including the teeth defin-
ing portions 13 completely and is solidified while being
pressed against the molding surface by the centrifugal force,
resulting in a cone body constituted with dense metal layers
having integral teeth 2 on an outer surface thereof as shown in
Fig. 5. Since the centrifugal ~orce produced around the vicin-
ity of the axis 11 is small, the density of metal portion
around the shaft may be low. However, that portion is removed
by machining to form a recess for receiving a bearing portion 4
for a bearing pin.
Fig. 2 shows another apparatus for performing the present
method. In this apparatus, a centrifugal casting mold 20 has a
plurality of pouring passages 22 extending radially from a ro-
tation center 21 and a corresponding number of cone casting
molds 23 connected to outer ends of the pouring passages, re-
spectively, with axes of the molds 23 being matched with
axes of the passages 22, respectively. Each of the cone
casting molds 23 has the same molding surface as that of the
mold in Fig. 1. A pouring gate is connected to the rotation
center 21.
By pouring molten metal to the rotation center 21 while
rotating the mold 20 at a high speed, the molten metal is pres-
sure-injected through the passages 22 to the cone molds 23, as
a result of which a plurality of cones each having the con~igu~
ration shown in Fig. 5 can be obtained simultaneouslyO When a
permanent type mold such as metal mold is used as the mold 10
l~G~735
or 23, the manhour of preparing sand-moldings may be eliminated
for subsequent moldings.
It may be possible to hard-face the teeth of the cone
thus manufactured. In such case, there is no need of machine
cutting of the teeth having complicated configuration, which is
necessary for the conventional milled tooth bit. Therefore, it
is possible to substan~ially reduce the number of manu~acturing
steps.
Fig. 3 is a vertical cross section of a casting mold to
be used in p~rforming the second method of the present inven-
tion. In Fig. 3, a casting mold 30 has a molding surface 32
composed of a cone defining surface portion and teeth defining
surface portions and the molding is performed by pouring a mol-
ten metal while rotating it around an axis 31 of the mold.
In manufacturing a cone with using the mold 30, inserts 3
of highly hard alloy such as tungsten carbide which form the
teeth 2 are preliminarily prepared and disposed in recesses 33
of the mold 30 corresponding to the teeth 2, respectiveIy, with
the inserts being supported such that root portions 3a thereof
are protruded inwardly of the cone defining surface 32 of the
mold 30. The centrifugal molding is performed thereafter as in
the previous case. Therefore, the root portions 3a of the in-
serts 3 are embedded in the cone body 1 as shown in Fig. 6. In
this case, the molten metal is forced to the surface 32 and
outer surface of the root portions 3a of the inserts 3 and so-
lidified under centrifugal force, the inserts 3 are reliably
supported by the cone body 1 having its surface defined by the
cone defining surface 32.
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When the root portion 3a of the insert 3 is shaped effec-
tively to prevent a drop out thereof from the cone body, the
reliability of insert holding is improved.
The machining of a hole 4 for arranging the bearing por-
tion after molded can be performed in the same way as in the
previous embodiment.
Figs. 4a to 4e show examples of the root portion 3a of
the insert 3, which may improve the reliability of insert hold-
ing effect of the cone body, respectively. In Fig. 4a, the in-
sert 3 takes on a conical form having an expanded root portion
3a. In Fig. 4b, the insert 3 is similar in shape to the insert
in Fig. 4a, except that a lower end face thereof is recessed as
shown by 3b. Since the highly hard alloy forming the insert 3
in expensive, the example shown in Fig. 4b is advantageous eco-
nomically. In Fig. 4c, a wall portion of the root portion 3a
of the insert 3 in Fig. 4b, which is defined by the recess 3b,
is cut away partially to form a plurality of legs 3c. This
example is more advantageous economically than the example in
Fig. 4b. In Fig. 4d, the root portions 3a of the insert 3 is
formed with a flange 3d and, in Fig. 4e, the root portion 3a is
formed with a plurality of annular grooves 3e. The corner por-
tions of root portion 3a are rounded in order to prevent crack-
ings of their material.
The shape of the root portion of the insert may be any
according to the mold of insert. Since the root portion of the
insert is embedded in the cone body during the molding thereof
with molten metal, the insert can be fixedly secured to the
cone body even if the root portlon thereof has a complicated
shape.
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735
Although the centrifugal casting has been described in
molding the cone with molten metal, any other pressure-casting
method such as die-casting can be used for this purpose. In
such case, when a metal mold is used it is possible to cool
casted metal rapidly. This is effective to prevent minute gaps
between outer surfaces of the root portions of the inserts and
the cone body from being produced due to shrinkage of metal
during a cooling period.
It is now described the third method of the present in-
vention with reference to Fig. 7. In Fig. 7, when a molten
hard metal is poured into a casting mold sech as a mold lO hav-
ing a molding surface 12 including a cone body surface and
teeth surface portions as shown ln Fig. 1 and a centrifugal
molding is performed, the molten metal 14 pressingly fills the
teeth portions 13 of the mold lO and solidified inwardly from
portions thereof which are in contact with the surface of the
mold. When a molten tough metal for the cone body is poured
before the hard metal is not completely solidified, the molten
tough metal is urged to a portion of the hard metal in the
tooth defining portion 13 which is separated from the surface
of the portion 13 and not solidified yet, by the centrifugal
force and the tough metal and the hard metal are metallurgical-
ly integrated together with and solidified. Thus, a cone hav-
ing teeth each of which has a hard metal cover layer having a
predetermined thickness measured from a tip of the tooth.
, Describing the fourth method of the present invention
with reference to Fig. 8, a tooth piece 15 is suitably sup-
ported in each of a molding surface 13 of a casting mold lO,
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'735
which corresponds to a tooth, such -that there is a gap between
an outer surface of the tooth piece 15 and the molding surface
13 and the tooth piece 15 protrudes slightly from a molding
surface of the casting mold 10, which corresponds -to a surface
of a cone body. The tooth piece 15 is of a tough metal similar
to a cone body material.
Then, a predetermined amount of a molten hard metal 14 is
poured into the mold 10 and a centrifugal casting is performed.
The hard metal 14 fills the gap between the tooth piece 15 and
the mold surface 13 and is solidified. Then, a centrifugal
casting of the cone body is performed by pouring the molten
tough metal into the mold 10. During the casting of the cone
body, the root portions of the tooth pieces 15 which protrude
from the milding surface of the cone body are surrounded by the
molten metal and melted together and then solidified. As a
result, a drill bi-t cone is obtained which has teeth whose por-
tions protruding outwardly from the cone body defining surface
are covered completely with the hard metal and having a core,
i.e., the tooth pieces 15 whose portions protruding inwardly
from the cone body defining surface are integrated completely
with the cone body and which is superior in mechanical strength
and performance.
In the third and fourth methods of the present invention
described as above, the centrifugal casting apparatus to be
used is not limited to that shown in Fig. 1. Instead thereof,
it may be possible to use the apparatus shown in Fig. 2 or
other pressure casting apparatus than the centrifugal type may
be used.
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